Prostate cancer continues to be a significant health problem, being the second most common cause of cancer-related death among American men. Local recurrence of prostate cancer is the most frequently detected failure of primary treatment, which propels subsequent treatment regimens onto an aggressive orbit, with the primary objective being to stop the tumor from spreading, otherwise the patient will rapidly develop a life threatening condition. Studies have shown that thermal ablation is helpful in the management of locally recurrent prostate cancer, either as a sole modality or as a preadjuvant sensitizer for external beam radiotherapy. The applicants have demonstrated in-vivo on canine subjects that high intensity interstitial ultrasound (HIIU) is appropriate for highly conformal delivery of cancer-killing thermal dose to the prostate. As a natural continuation, a computer-controlled ultrasound image guided system is proposed for transrectal ultrasound image-guided delivery of treatment using high intensity interstitial ultrasound. The goals for Phase-I are to (1) develop a transrectal needle placement mechanism, (2) package an existing HIIU device in flexible needle, and (3) prove feasibility of the prototype device on ex-vivo animal models under image guidance. The goals for Phase-II are to design and implement a computer-integrated system, with advanced image guidance, visualization, planning, and real-time quality control functions. The unique attribute of the proposed system is that the physician can "see" the relationship of the ablator needle to the ideal thermal dose plan in realtime and quickly accommodate the spatial distribution of energy to compensate for any discrepancy. The most appealing element of this system is the prospect that the outcome of tissue ablation treatments would no longer depend decisively on the geometrical accuracy of device placement, because reasonable spatial inaccuracies could be safely compensated by the electronic spatial power distribution control built in the acoustic energy delivery mechanism. The resulting system will be tested on canine subjects and in a limited manner on human patients. The endpoint of the proposed research is a system for which IRB approval can be sought to conduct clinical trials.